Rotational rate sensors in which a first and a second Coriolis element are arranged on the surface of a substrate are discussed in U.S. Pat. No. 5,728,936. The Coriolis elements may be induced to vibrate along a first axis. The deflections of the Coriolis elements due to a Coriolis force along a second axis, which is likewise parallel to the substrate, may be verified.
German Patent No. 198 32 906 discusses a capacitive rotational rate sensor made up of a flexibly supported, mirror-symmetrically designed seismic mass, on which electrodes are fastened in a comb-like manner. At least two groups of comb-like counterelectrodes may be provided, arranged in mirror symmetry, which may be each fastened to a carrier and engage between the electrodes fastened to the seismic mass. The carriers of the counterelectrodes may be fastened only in the vicinity of the axis of symmetry at the closest point on a ceramic carrier. A frame may also be provided on which the seismic mass is fastened via two leaf springs. Two actuators may be used for the excitation of vibrations of the frame, which has integrated vibratory springs and which may be fastened on the ceramic carrier at at least two points of attachment.
European Patent No. 0 775 290 discusses a rotational rate sensor made up of at least two vibrating masses, which are connected to each other via a spring element to form a system capable of vibrating, which is supported on a substrate. Also provided are actuators for inducing vibrations, as well as at least one sensing element for the detection of the Coriolis force. The spring elements and the vibrating masses are positioned and designed in such a manner that the system capable of vibrating is only able to execute vibrations in at least two vibration modes parallel to the plane of the substrate, one mode being used as excitation mode of the vibration excitation and the second mode, possibly orthogonal to it, is excited as the detection mode upon rotation about an axis perpendicular to the substrate to the Coriolis forces.
M. Lutz, W. Golderer, J. Gerstenmeier, J. Marek, B. Maihöfer and D. Schubert, A Precision Yaw-Rate Sensor in Silicon Micromachining; SAE Technical Paper, 980267, and K. Funk, A. Schilp, M. Offenberg, B. Elsner, and F. Lärmer, Surface-Micromachining of Resonant Silicon Structures, The 8th International Conference on Solid State Sensors and Actuators, Eurosensors IX, Stockholm, Sweden, Jun. 25–29, 1995, pp. 50–52, discuss other rotational rate sensors.
One disadvantage of the known rotational rate sensors is the sensitivity of the structures with respect to interference accelerations, particularly with respect to angular accelerations about the sensitive axis, as well as with respect to the insufficient robustness of the structures.
One reason for the sensitivity with respect to interference accelerations may be particularly founded in the low working frequency of these rotational rate sensors (1.5 kHz to 6 kHz), since in this frequency range interference accelerations may occur in the motor vehicle which have non-negligible amplitudes.
A second reason may be linked to the functioning principles of rotational rate sensors. In the case of a certain sensor type, besides a (desired) external rotational speed about the sensitive axis, a measuring signal may also be triggered by a rotational acceleration about the same axis. Therefore, the known rotational rate sensors may be particularly sensitive to this kind of interference acceleration.
The low working frequencies may also be a reason for the inadequate robustness of the rotational rate sensors, particularly as regards falling protection. A further reason for the inadequate robustness may be involved with a complicated process control, for example, a combination of bulk and surface micromechanics.